Adrian Mulholland

Molecular Structure and Bonding

p Electrons in Conjugated Organic Molecules

Lecture 1-2

Hückel Approximate MO Theory for conjugated hydrocarbons. (Atkins & De Paula, 7^th Edn. pg. 433)

Summary

• The Hückel Approximations for conjugated p-electron systems.

• These approximations lead to easily solvable equations for the energies and p molecular orbitals

• How to apply Hückel theory to the calculation of p molecular orbitals for any conjugated system. Example: Butadiene.

· The relationship between the nodal structure of the molecular orbitals and the energy.

• The concept of delocalization energy.

• Cyclic conjugated polyenes (e.g. benzene)

• The Geometric (or ‘Circle’) Method for finding the MOs of cyclic conjugated polyenes

• Aromaticity: stability of aromatic molecules. The (4n+2) rule.

Next: the Hückel Approximations